What Flowmeter calibration techniques do Litre Meter use?

Essentially, there are three separate calibration methods that Litre Meter have in-house to calibrate a range of flowmeters.  As the fluids can vary from water to thick oil and the flows range from a few millilitres per hour to 1,000 litres per minute, there are not only three calibration methods but 10 rigs in total, all traceable to National Standards.

The most common calibration method for Litre Meter is gravimetric with flying start and stop.  This method, as the names suggests, records the weight to provide a mass flow. Frequently, this is converted to a volume flow after determination of density.  After that, the use of master meters is popular for higher flows, above a few litres per minute. Finally, where the flow rates are outrageously low – i.e. just millilitres per hour – Litre Meter have developed a volumetric pistonless design – the FlowLabPro.

Gravimetric Flying Start-Stop

Most Litre Meter flowmeters are calibrated using a gravimetric method.  A flow rate is established through the flowmeter with the output flow returning to the main reservoir.  At the commencement of test, the output flow is diverted into a weigh tank.  When sufficient volume of fluid has been collected in respect of that particular flow rate, the output flow is diverted to the main reservoir once more.  The time for the volume of fluid to be collected is recorded, together with the number of pulses produced by the transmitter.  The density of the fluid is determined at time of calibration.  Volume divided by time equals flow rate.  The number of pulses divided by volume equals the pulses per litre Meter Factor.  The calibration certificate is prepared from a table of these values.  If on-site calibration is required and a known volume of fluid flow can be established, then the same calculations apply to reproduce the calibration certificate.

Significant effort should be spent ensuring that the start and stop timing accurately reflect when flow is being weighed and that the speed of changeover is maximised. With modern, accurate weigh scales and timing the stop/start transitions are where precision improvements are made. Litre Meter have developed a simple program that enables quick monitoring of diverter performance and aids the operator in adjusting the timing.

When pulse rates are very low, such as in the VFF and some other positive displacement flowmeters, the flow rig electronics are altered such that a calibration run commences on a pulse and finish on a pulse. For example, a calibration run is dialled in requiring 60 pulses.  The operator starts the test with continuous flow running through the MUT. When the next pulse is sensed the diverter operates and the scales begin weighing the fluid. After 60 pulses pass the diverter switches back and measurements are taken. There will be 60 pulses, a specific weight and a specific time enabling the calculation of flow rate and pulses per mass unit. With an sg reading from a suitably accurate densitometer then the rate can be calculated in volumetric terms and the pulses used to calculate pulses per litre.  There is no uncertainty in the number of pulses i.e. whether the next pulse was about to arrive or had just been. This is usually an uncertainty of up to two pulses.  There is an unknown time at Start of diversion but this is somewhat equalled out at the Stop side. Good calibration of the start/stop sequence can almost eliminate this unknown.

Master Meter

As the flow rate increases the compactness of the Gravimetric method with it’s diverter starts to die away and the rigs become very large. At Litre Meter we have a good crossover between the upper end of the gravimetric to the lower end of the master meter which provides some flexibility and confidence.  For water the gravimetric rigs are suitable for flows up to 30 l/min and the master meters commence at 1 l/min. For oils it’s 10 and 0.1 respectively. Without the knife-edge start of the gravimetric flying start (above) the master meter technique pivots (sorry for the pun) around dual chronometry. The Meter Under Test produces a pulse train simultaneously with the Master Meter but at a different frequency.  The computer program starts and stops the test period depending on the preset length of test and the number of pulses desired.  The preset length is then subtly adjusted so that a precise number of pulses is used. Further analysis of the MUT pulse rate counts the number of pulses, and more importantly, determines the fractional number of pulses at the start and end of test.  Finally, the test is repeated at least three times at each flow rate.  These are installed in a continuously running system, in a loop, thus enabling multiple tests in quick succession.  The pump or valve position is then altered to process all of the desired flow rate range in a suitable number of steps.

Piston-less piston prover

For investigation of very low flows our traditional gravimetric rigs were unable to control and/or develop low flows consistently. For the LF03 the low flows are actually lower than the leak flows through the valves or our then smallest system. A change of method was required.  Starting with a series of pumps a method was instigated using a rising column of fluid being monitored by an accurate height sensor.  With a variety of column diameters a wide range of flow rates can be generated and measured accurately.  Pulse interpolation is used in much the same way as for dual chronometry, above, except that the MUT and the height sensor are the two sources of pulses. All of the components including a choice of fluid reservoirs are together in one enclosure, temperature controlled, to maintain consistency.  Up to 4 rotors and chambers can be calibrated together over the required flow rate range enabling calibration to continue overnight, unsupervised.  Additional software programs can quickly determine minimum achievable flow which significantly speeds up parts selection for our LF and ULF calibration levels.

 

 

Pelton Wheel flowmeters

Litre Meter manufacture and distribute an enviable range of flowmeters. From the low flow robustness of the VFF positive displacement meter to the precision of the Tricor Coriolis range, Litre Meter have a solution to your tricky measurement application.  Call our engineers now to receive the best advice on meter selection and application.

LM & MM Pelton Wheel

LMX Pelton Wheel
Stainless Steel Pelton Wheel LMX Flow Meter

The LMX series, pictured, was designed from the outset to meet two simple parameters: a pressure rating of 100 bar coupled with a temperature rating of 100°C. End couplings are either ½”NPT or BSP with built-in straight lengths of pipe. As a bonus, the minimum fluid temperature can be -50°C and there are just 3 wetted materials. With 316 stainless steel, PTFE and sapphire in contact with the fluid there are few applications that it can’t handle. Flow rate abilities are selected by different internal jets enabling the same size body to measure from 0.004 l/min up to 65 l/min in just a few sizes.

Applications are numerous. The Pelton Wheel was originally developed with petrol and water in mind.  These are both low viscosity fluids and are measured regularly, often at low flow rates. The smallest range (LM003) is designed to measure from 4 millilitres per minute up to 60 ml/min. As the jet size increases the rangeability also increases. The LM05, for example, 0.02 to 1.3 l/min and the LM220 is a magnificent 0.1 to 28 l/min.

These wide ranges can be attributed to 3 significant design factors:

  • Wide bladed pelton wheel design for maximum impulse
  • Sapphire bearings for minimal friction
  • A no-drag sensor to enable lowest flows

With over 44 years’ experience in these meters we have optimised the bearing and sensor design for long life and high efficiency with remarkable linearity.

Calibration of a thermotechnical test stand

Measurements for approvals are taken under highly constant thermal conditions using an especially designed test stand.

The TRICOR Coriolis Mass Flow Meter TCM 0325

The TRICOR Coriolis Mass Flow Meter TCM 0325 was integrated into the hot water circuit

APPLICATION The Thermotechnical Institute (WTI) of the Mannheim University of Applied Sciences is one of three centres of expertise in Germany appointed for the type approval and DIN testing of heating cost allocators (according to Section 5 of the Heating Costs Ordinance). Measurements for approvals are taken under highly constant thermal conditions using a specifically designed test stand. The specimens (heating cost allocators) are mounted on a radiator. Hot water is circulated through the radiator. The supply and return temperature, as well as the mass flow and volume flow of the hot water, have to be measured with high accuracy. A permanently installed external device is used for measuring the volume flow according to the Coriolis principle.

TECHNICAL DATA

Medium Hot water
Temperature 68-194 °F (20-90 °C)
Pressure 1.5-15 psi (0.1-1 bar)
Measurement range 5-200 l/h

PRODUCT A TRICOR Coriolis Mass Flow Meter TCM 0325 for liquids and gases.

CHALLENGE For accreditation as an internationally recognized test laboratory according to DIN EN 17025, the flow meter that is used has to be calibrated using a DAkkS calibrated measurement standard; a relatively low flow rate has to be measured as accurately as possible over a wide range of 5 to 200 litres per hour. Since the hot water contains suspended matter in the form of tiny lime and rust particles, the measuring device should not have any components that are moveable or susceptible to deposits. Furthermore, the flow meter that is used has to ensure the required accuracy across the entire measuring range for the medium being used, with calibration according to DAkkS standards. The applicable accuracy limit was less than 2 % of the measured value.

SOLUTION The TRICOR Coriolis Mass Flow Meter TCM 0325 was integrated into the hot water circuit and serves as a reference for the internal calibration of the existing, permanently installed flow meter. The TCM 0325 supports flexible and portable operation. It is calibrated at the prescribed regular intervals according to DAkkS standards in KEM’s own calibration laboratory certified according to DIN EN ISO/IEC 17025:2005.

BENEFITS

  • Reliable, reproducible measurement results
  • Coverage of the entire calibration measurement range with just one measuring device
  • High measuring accuracy
  • Flexible and portable application
  • Calibration and certification to DAkkS ISO 17025 standard

Why should I measure Corrosion Inhibitor (and how)? – our experts explain:

It is essential to measure Corrosion Inhibitor, accurately and continually.  With the correct system, pipeline life can be extended for many years.

Corrosion Inhibitor, sometime abbreviated to CI, is manufactured by various chemical companies to inhibit (to stop or slow) the rate of corrosion inside a pipeline as it carries a flowing product. In the normal Litre Meter context, a company that is heavily involved in Oil & Gas flow measurement, the flowing product is crude oil, straight out of the well.

Depending on the chemistry of the well, a specific inhibitor will be recommended or will be formulated to treat the oil in an optimum manner. As each well is different a large variety of solutions can now be chosen.  For flow measurement, the two main variables are flow rate and viscosity. Usually the fluids are compatible with stainless steel but sometimes higher specification steels or more exotic materials like titanium are required.

If not enough CI is present in the oil then the pipe walls will be corroded and will eventually lose their integrity and then fail. If too much is injected then costs can quickly mount up. Not only is the raw inhibitor expensive but also the tanks will need replenishing more often. Worse still, the refineries will charge dollars per barrel to remove the excess before the crude oil can be processed.

Corrosion Inhibitors prevent corroded pipes

Relying on pump speed, combined with calculation of volume per stroke, is insufficient for full flow assurance. The pump motor can be going but that’s no guarantee the fluid is flowing or that the amount is correct. Full flow measurement is necessary. Optimal meter selection, by experts, ensures good measurement over the full range of flows that the process can experience. It’s not unusual for the flow rate to vary by a factor of a 100 during the life of a well so a wide ranging flowmeter system is a good choice.

The VFF positive displacement flowmeter has been developed over the years to meet all the requirements of chemical injection and more.  They all offer:

  • Excellent materials, for long life, compact and lowest weight.
  • Repeatability – what happens now is the same as a year ahead
  • State of the Art instrumentation – mostly in SS with 4-20 and HART and linearisation.
  • Flexibility, changeable internals for gross range changes, high pressure ratings as standard, etc

Corrosion Inhibitor measurement = VFF

Extending the flowmeters calibrated range – an expert view

It’s not an uncommon request.  When the enquiry comes in the client thinks the required range will be 1 to 10 but, once installed, it’s clear that he should have stated 2 to 20.  Then, the question is: what do we do?

First: it’s unlikely that the range can be extended beyond the meter maximum rated flow rate.  Some flowmeter principles can cope with excessive flow rates, probably at the expense of pressure drop, but most can’t.

Second: Consider the magnitude of change and the expectation of accuracy. If it’s a change from 1 to 10 to 1 to 11 with a 5% accuracy requirement when the maximum rate is 12 then that’s an easy one – check with the factory on how the range can be changed within the instrumentation but the range extension will be OK. On the other hand, if it’s a ±0.2% meter then it’s unlikely that any range extension will be within that value without a return to the factory for recalibration.

Here’s an example:

The client had purchased an LF03 VFF positive displacement meter for the measurement and control of corrosion inhibitor.  The viscosity was 55cP and, although the meter is capable of 18 litres per hour, had specified an operational range of 0.2 to 2.3 l/h which we calibrated over.

A year later we had a request for a range change – could they up the calibration range to 5.6 l/hr? Of course, yes. Could we provide a statement to this?  See below:

VFF Flowmeter Extended Range Accuracy – 50cP viscosity

The original calibration for meter VFF5112 was up to 2.3 l/hr on 55cP. Litre Meter have analysed the last 17 LF03s calibrated at or around 50cP and can confirm that re-ranging to 5.6 l/hr will have only a minor effect to system accuracy.

VFF Analysis:

It can be seen from the aggregated performance curves above that extending the flow rate above 2.3 l/hr up to 7 l/hr produces little change in the meter linearity. We would suggest that, in the absence of any higher flow rate information above 2.3 litre per hour, that the meter is unlikely to be outside of ±2% of the 2.3 l/hr pulses per litre value up to 7 litres per hour. Increased confidence and accuracy can be obtained by recalibration.

Linearisation:

Litre Meter produce a document LM0688 “Technical Description – Linearisation” that explains the linearization process and the flow rate versus pulses per litre table. Also here.

KEM Küppers flowmeters include the ZHM round gear PD meter

Litre Meter are the exclusive UK distributors for KEM Küppers.  These include the ZHM, SRZ positive displacement, HM turbine and the Tricor coriolis series. Sign up for FlowSight, the Litre Meter newsletter.

KEM ZHM01/3 gear meter
KEM ZHM01/3 gear meter

The ZHM series is highly engineered round gear PD flowmeter suitable for a slew of different applications such as hydraulic oil, automotive paint and chemical dispense measurement.

  • From 0.002 to 1 LPM to 1,000 LPM
  • Ratings to 315, 414, 690 bar and higher
  • Accuracy: ±0.5% of reading or better
  • Repeatability: ±0.05% of reading
  • Can be installed in any orientation
  • Cartridge, compact & aluminium options.

All of these units are manufactured in Germany by Litre Meter’s sister company, KEM Kueppers GmbH.

 

 

Reverse flow measurement – an expert view

Most flowmeters are setup for forward flow measurement. That is, they have a preferred direction for operation and that is adopted by the manufacturer/designer and advised to the customer.

Some flowmeters are symmetrical in the forward and reverse direction and will work in the reverse direction, too. Some are symmetrical and may not function or function well, due to meter design or principle, in reverse.

Finally, some meters may detect that the flow is in reverse and, better still, measure in either direction to the same accuracy.

We use the term flowmeter generically. When discussing flow direction and measurement we should consider the instrumentation as well as the flow sensor itself.

Distinctions:

Type A – not designed for Reverse flow, may cause damage:
Type B – can accept reverse flow, no detection
Type C – can accept reverse flow, detects direction of flow
Type D – Can accept reverse flow, measures accurately but doesn’t output direction
Type E – Accepts reverse flow and provides flow velocity and direction

B, C, D, E may need special instrumentation to extract the desired information.  The type designation just helps us understand the designs – it isn’t used outside of this article.

Flowmeter element Type
Orifice plate B, C, D or E
Wedge B, C, D or E
Venturi tube B, C, D or E
Flow Nozzle B or C
Pitot tube B
Elbow meter B, C, D or E
Target meter B or C
VA A or E (E with a special meter)
Positive Displacement A, B, C, D or E depends on design and sensing
Turbine A, B, C, D or E depends on design and sensing
Pelton A, B, C, D or E depends on design and sensing
Vortex A or B
Electromagnetic B, C, D or E – most units would be E
Ultrasonic(Doppler) B, C, D or E – most units would be E
Ultrasonic(Time-of-travel) B, C, D or E – most units would be E
Mass Coriolis B, C, D or E – most units would be E
Thermal Mass Insertion B
Thermal Mass Capillary B
Weir A
Flume B

 

Litre Meter flowmeters

Pelton Wheel

The LM range have a jet (apart from the LM220 and LM330). With a jet concentrating the flow onto the rotor, a reverse flow is very inefficient and the rate of rotation is much reduced for the same flow. The 220 and 330 are broadly symmetrical in some models and have different pipe layouts in most versions. These have never been fitted with technology to provide direction.

The same can be said of the larger, orifice plate based, MM meter. The inlet and outlet holes to the pelton wheel chamber are much different in size, so function poorly in reverse. A sole MM was manufactured with two pelton wheels and two sensors facing in different directions. By comparing the magnitude of the signals it was simple to tell which direction was active.

VFF

All VFF (rotary piston positive displacement) meters are perfectly symmetrical in design with rotors able to rotate clockwise or anticlockwise. There are small differences in machining so there are small differences in meter performance forward and reverse. There is a prescribed forward direction (purely for consistency) but the client can select the other direction as forward.

With a standard sensor the output is the same whether the flow is forward or reverse – just a series of pulses. When two sensors are fitted then the direction and magnitude of flow can be determined if the right instrumentation is used.

There are two suitable instruments used by Litre Meter and at least one system used by clients with varying degrees of sophistication. Sometimes two sensors are fitted for redundancy purposes. The instrument monitors one sensor. After a certain time period, if there isn’t a pulse attention is switched to the other sensor. The period is set to be a few seconds longer than the frequency for lowest flow achievable or the clients lowest expected flow.

Litre Meter use two sensor setups both based on reed switch sensing of the magnet in the VFF rotor. Litre Meter are developing a 3-D magnetometer based field sensor that can determine the position of the rotor in the chamber for finer pulse output.

If reed A switches before reed B then direction is forward. If B before A then direction is reverse.

The two reed switch setups are similar in concept but packaged differently. The original reed switch is situated in a sensor hole. When two reeds are used there are two parallel holes generally situated along the radius of gyration of the magnet. They are spaced to produce a clear lead or lag depending on rotor direction. The Fluidwell F115 is designed to interpret the lead/lag to produce a display with directionality.

With the introduction in 2015 of the CIFM versions of the VFF and the Litre Meter FlowPod the sensor was repackaged, with two reeds as standard, in an M8 stainless sensor body. Only one sensor hole is required as the reeds are side by side. The F115 and FlowPod can both interpret the CIFM sensor output.

F115

Fluidwell manufacture a wide range of instrumentation which Litre Meter have used since 2002. The F115 version is specifically designed for directionality. It does not have linearisation.

Description

The flow rate / totalizer model F115-P is a microprocessor driven instrument designed to show the flow rate, the total and the accumulated total. This model is able to detect the flow direction and to show a positive or negative flow rate, the totals for both directions and the cumulative totals.
This product has been designed with a focus on:

  1. ultra-low power consumption to allow long-life battery powered applications (type PB/PC),
  2. intrinsic safety for use in hazardous applications (type XI);
  3. several mounting possibilities with aluminum or GRP enclosures for harsh industrial surroundings;
  4. ability to process all types of flowmeter signals;
  5. transmitting possibilities with analog / pulse and communication outputs.
Flowmeter input

Two sensors with a phase difference of 90 or 270 degrees, can be connected to the F115-P.

Standard outputs
  1. Pulse output to transmit a pulse that represents a totalized quantity as programmed.
  2. Negative / positive pulse output indication – i.e. a flag.
  3. Linear 4-20mA analog output to represent the actual flow rate as programmed. The 4-20mA signal limits can be tuned.

FlowPod

Description

The FlowPod was designed from the outset with the CIFM sensor which is fitted with two closely positioned reed switches in one M8 stainless steel package. They are positioned in the flowmeter to provide a two separate pulses along the path of the spinning rotor. They are fairly close together such that there is a distinct time difference between reed A and B depending on direction.

In most installations the second reed is for redundancy purposes. The FlowPod monitors reed A. After a certain time period, if there isn’t a pulse, attention is switched to reed B. The period is set to be a few seconds longer than the frequency for lowest flow achievable or the lowest expected flow.

For directionality the FlowPod monitors reed A and B and interprets lead and lag to determine flow direction. Within the software forward direction can be set as ‘A before B’ or vice versa. Redundancy is still offered, although, of course, without direction.

Linearisation is standard on the FlowPod. The curve of flow rate versus frequency is similar in forward and reverse.

 

The drive to save weight

There was a very interesting article about Shell in last months Fortune. It explains how Shell were approaching the next decade and building 4 different scenarios of oil price and availability and their investment reactions to those.  I’ve included the link at the end of this article.  Sign up for FlowSight, the Litre Meter newsletter.

It also detailed the effect on their platform design when the oil price suddenly reduced.  The most striking image is of two platforms designed in different eras.  Appomattox will soon be active in the Gulf of Mexico so would have been designed in 2013 with a Final Investment Decision (FID) in July 2015.  Vito was designed in early 2014, when oil was at $100.  By 2015, when the price had slipped, Vito was looking bulky. In early 2016 it was decided to slim it down to be profitable at $40.

A radical design overhaul slashed the top weight over the next year, from 40,000 tons to 8,900 tons. The shell team right-sized Vito, for a world of ‘peaking oil demand’.

The similarities with Litre Meter developing the FlowPod instrument seem tenuous – and we don’t have meters on either platform, which is unusual. But, the FlowPod was developed over 12 months from the original FPod Exd flow display.  The prime motive was size reduction and improved performance.  With that, and unclear at the start of the process, was a beneficial reduction in meter size and weight into the bargain.

The original purpose of the redesign was two-fold: firstly, to reduce the size of the instrument enclosure – mounting them remotely from the meter produced some unexpected challenges for our clients from time-to-time; secondly, to replace on obsolescent internal electronic component. It transpired that the new component was even bigger than the old one so a thorough instrumentation re-design was discussed, eliminating the large isolator and taking the benefit of a reduced enclosure size. This wasn’t an easy task and soon we were down the road of a ground-up redesign encompassing the traditional sensor which now had to be part of an Exd system.

With a new sensor every cap was also redesigned and there was a knock-on effect to the VFF body. We coupled this refinement with a desire to provide our customers with more standard meters ‘off-the-shelf’ shifting our traditional 80% bespoke/20% standard to 80/20 standard design vs custom, offering better availability.
When the dust had settled the new VFF, although having the same flow rate ranges, had a standardised Pressure Balanced Chamber design with a redesigned sensor, a compact display dubbed FlowPod certified Exd and over 114,000 different standard designs.
Litre Meter have analysed our customer’s requirements which has resulted in the various meter sizes being available in most appropriate connection sizes and styles. For example:

VFF flowmeter sizes and selected threaded connections.The sheer range of choice, which also encompasses body & cap materials, seal materials and instrumentation has effectively designed out the need for customization. Drawings are available for over 114,000 different VFF configurations – including
  • General Arrangement,
  • Parts List and
  • Lifting Diagrams, together with a
  • STEP file, allowing instant modelling.

Lead times are reduced, enabling customers to bring their projects to fruition earlier. There is a dedicated program that enables Litre Meter and their distributors to select and configure flowmeter solutions quicker and more accurately.

All the VFF range are designed around the Pressure Balance Chamber.  Cap and body sizes have been rationalised and minimum pressure ratings increased. For example, the most popular 1/2″NPT female body is now rated to 530 bar rather than 414 bar previously, increasing it’s usability just by varying bolting material.

Here are two identically ranged meters with 1/2″NPT female connections:

The older FPod on the left dwarfs the more compact FlowPod and rationalised body and cap.

Instrument weight plummets from 5 kg to 1.2 kg and display enclosure diameter reduces from 6.5 to 3.5 inches.  Stainless steel is now standard.   Here’s a quick comparison:

FlowPod benefits

We think this clearly demonstrates Litre Meter’s commitment to continuous improvement, matching Shell’s dramatic reductions on the Vito project. Fortune article.

 Sign up for FlowSight, the Litre Meter newsletter.

Upgrading your FPod to FlowPod – a simple guide

The drive to save weight from the flowmeter experts

There was a very interesting article about Shell in last months Fortune. It explains how Shell were approaching the next decade and building 4 different scenarios of oil price and availability and their investment reactions to those.  I’ve included the link at the end of this article.  Sign up for FlowSight, the Litre Meter newsletter.

It also detailed the effect on their platform design when the oil price suddenly reduced.  The most striking image is of two platforms designed in different eras.  Appomattox will soon be active in the Gulf of Mexico so would have been designed in 2013 with a Final Investment Decision (FID) in July 2015.  Vito was designed in early 2014, when oil was at $100.  By 2015, when the price had slipped, Vito was looking bulky. In early 2016 it was decided to slim it down to be profitable at $40.

A radical design overhaul slashed the top weight over the next year, from 40,000 tons to 8,900 tons. The shell team right-sized Vito, for a world of ‘peaking oil demand’.

The similarities with Litre Meter developing the FlowPod instrument seem tenuous – and we don’t have meters on either platform, which is unusual. But, the FlowPod was developed over 12 months from the original FPod Exd flow display.  The prime motive was size reduction and improved performance.  With that, and unclear at the start of the process, was a beneficial reduction in meter size and weight into the bargain.

The original purpose of the redesign was two-fold: firstly, to reduce the size of the instrument enclosure – mounting them remotely from the meter produced some unexpected challenges for our clients from time-to-time; secondly, to replace on obsolescent internal electronic component. It transpired that the new component was even bigger than the old one so a thorough instrumentation re-design was discussed, eliminating the large isolator and taking the benefit of a reduced enclosure size. This wasn’t an easy task and soon we were down the road of a ground-up redesign encompassing the traditional sensor which now had to be part of an Exd system.

With a new sensor every cap was also redesigned and there was a knock-on effect to the VFF body. We coupled this refinement with a desire to provide our customers with more standard meters ‘off-the-shelf’ shifting our traditional 80% bespoke/20% standard to 80/20 standard design vs custom, offering better availability.
When the dust had settled the new VFF, although having the same flow rate ranges, had a standardised Pressure Balanced Chamber design with a redesigned sensor, a compact display dubbed FlowPod certified Exd and over 114,000 different standard designs.
Litre Meter have analysed our customer’s requirements which has resulted in the various meter sizes being available in most appropriate connection sizes and styles. For example:

VFF flowmeter sizes and selected threaded connections

The sheer range of choice, which also encompasses body & cap materials, seal materials and instrumentation has effectively designed out the need for customization. Drawings are available for over 114,000 different VFF configurations – including

  • General Arrangement,
  • Parts List and
  • Lifting Diagrams, together with a
  • STEP file, allowing instant modelling.

Lead times are reduced, enabling customers to bring their projects to fruition earlier. There is a dedicated program that enables Litre Meter and their distributors to select and configure flowmeter solutions quicker and more accurately.

All the VFF range are designed around the Pressure Balance Chamber.  Cap and body sizes have been rationalised and minimum pressure ratings increased. For example, the most popular 1/2″NPT female body is now rated to 530 bar rather than 414 bar previously, increasing it’s usability just by varying bolting material.

Here are two identically ranged meters with 1/2″NPT female connections:

The older FPod on the left dwarfs the more compact FlowPod and rationalised body and cap.

Instrument weight plummets from 5 kg to 1.2 kg and display enclosure diameter reduces from 6.5 to 3.5 inches.  Stainless steel is now standard.   Here’s a quick comparison:

FlowPod benefits

We think this clearly demonstrates Litre Meter’s commitment to continuous improvement, matching Shell’s dramatic reductions on the Vito project. Fortune article.

 Sign up for FlowSight, the Litre Meter newsletter.

Upgrading your FPod to FlowPod – a simple guide

What’s in a typical flow meter datasheet?

First, let’s have a look at what might land on your desk.  Later, we’ll review it line by line. Sign up for FlowSight, the Litre Meter newsletter.

A typical datasheet relating to a flowmeter is given as below – this one is based on a NORSOK format:

Flowmeter datasheet – Norsok layout.

This one is for the same meter but based on an ISA format (a version used by Litre Meter which uses S20.25 as it’s base):

Flowmeter datasheet – ISA layout, describing the same flowmeter.

Norsok:

This is an approximate layout, typified by NORSOK.

1 General

1.01 Type – a description of the flowmeter, by trade name and basic principle

1.02 Manufacturer – manufacturer’s name.

1.03 Design Temperature Limits – maximum and minimum design temperatures in suitable temperature units (°C)

1.04 Design Pressure Limits – maximum and minimum design pressures in suitable pressure units (bar gauge)

1.05 Estimated Pressure Loss – pressure drop at a specific flow such as maximum in suitable units (millibar)

1.07 Face to face dimension – complete assembly length in millimetres, with a tolerance

1.08 Mounting – type of mounting, in this case, In-Line but could be insertion, clamp-on etc.

1.09 Weight – dry, without fluids – in kilogrammes

2 Instrument Characteristics

2.01 Calibrated Range – flow rate range that the unit will be calibrated over – and units

2.02 Characteristic – an appreciation that not all meters are necessarily linear – some are non-linear such as orifice plates where the pressure drop is related to the flow rate by a square law, in this case linear – and linearised.

2.03 Meter factor – an estimated value of the number of pulses per litre – or other volume or mass unit

2.04 Accuracy – with percentage bounds and either proportional to the actual reading or FSD (Full Scale Deflection)

2.05 Linearity – with percentage bounds and either proportional to the actual reading or FSD (Full Scale Deflection)

2.06 Repeatability – with percentage bounds and proportional to the actual reading

2.07 Max Range limit – not necessarily the same as the maximum calibrated flow – describes the capabilities of the flowmeter

3 Meter Body

3.01 Nominal Size – normally relating the meter body size to the pipe size

3.02 Manufacturer model number – to precisely define the scope of supply

3.03 Process connection size and type – Size and flange or thread type, for example

3.04 Pressure rating – the rating of the flowmeter body in comparable units to 1.04

3.05 Face to face dimension – will match 1.07 in most cases

3.06 Body inner diameter – where appropriate

3.07 Sour service specification – nominated when appropriate – ISO or NACE in this example

3.08 Material, body – A specification for the material of the flowmeter body i.e. the main part of the meter

3.09 Material, Raised –

3.10 Protective coating/color

3.11 Other

4 INTERNAL

4.01 Type – such as rotor and chamber or another description of the flowmeter internals and principle

4.02 Material, shaft – if any

4.03 Material, support – if any – this might refer to a turbine flowmeter part

4.04 Material, rotor

4.05 Material, bearing – if any, may include material and type

4.06 Material, Seal – not just the materials but may include seal type

4.07 Material, pick-up – i.e. sensor material, wetted, or not

4.08 No of pick-ups

4.09 Other

5 FLOW STRAIGHTENER

5.01 Type

5.02 Material

5.03 Connection

5.04 Other

6 METER TUBE

6.01 Material

6.02 Connection up/downstr.

6.03 Up/downstream length

6.04 Tube inner diameter

6.05 Other

7 STRAINER

7.01 Type

7.02 Body/mesh material

7.03 Connection

7.04 Other

8              TRANSMITTER

8.01        Manufacturer model no

8.02        Mounting

8.03        Max distance meter/trans

8.04        Cable connection

8.05        Cable entry

8.06        Dimension

8.07        Material

8.08        Enclosure protection

8.09        Ex. classification

8.10        Protective coating

8.11        Indicator

8.12        Tamb

8.13        Totalizer

8.14        Output signal (note 9.02)

8.15        Communication

8.16        Recommended loop voltage

8.17        Transmitter loop voltage drop

8.18        Max loop current (fault condition)

8.19        Other – in this case describes more of the hazardous area ratings and standards – CSA, IECEx and ATEX

Measuring Sodium Hypochlorite in Hazardous Areas

Sodium Hypochlorite

Sodium hypochlorite is a green/yellow liquid with the characteristic smell of chlorine. It was first used as a bleaching agent and was then discovered to be effective in controlling wound infections. Subsequently, it is most commonly known as household bleach. The solution exhibits broad spectrum anti‐microbial activity and is widely used in healthcare facilities in a variety of settings. It is usually diluted in water depending on its intended use. Sign up for FlowSight, the Litre Meter newsletter.
In the chemical injection arena, it is common to inject sodium hypochlorite into sea water. Sea water can contain dissolved oxygen, bacteria and solids. These can affect an oil reservoirs life. Hypo is used as a bactericide whilst filters take care of the solids. Hypo is aggressive before it is diluted in the sea water and therefore requires some specialized devices in terms of wetted materials. Litre Meter have been manufacturing flowmeters since 1975.
We’ve always concentrated on the harder margins of metering typically at low flows and/or at high pressure. For this application note Litre Meter illustrate two solutions to this application based on <20 % solution. Download brochure.

Sodium Hypochlorite Flowmeters ‐ Applications and Rates ‐ VFF

The VFF has successfully metered fluids such as oils, hydraulic fluids, corrosion / wax / demulsifier / pour point dispenser /scale / hydrate inhibitors, biocides, oxygen scavengers, etc. for over 30 years. Meter bodies are produced in a variety of high grade materials which offer good chemical and environmental resistance. For sodium hypochlorite, Litre Meter recommend Titanium for the body and chamber with carbon graphite for the actual rotary piston. This ensures maximum compatibility, life and accurate response. The magnet is either encapsulated in titanium or PTFE.

VFF Flowmeter Sizes and Connections.

Applications for flow‐rates as low as 0.5 litres per hour have been supplied. Normal minimum flow rates depend on operating viscosity. In this case, viscosity is assumed to be between 1 and 2.5cP. Using the smallest VFF with carbon graphite rotor (LF15) and calibrating on water, which has a lower viscosity than NaOCl, a range of 0.5 to 40 L/hr is achieved. The meters range in size from the smallest titanium body, LF15 – 40 L/hr, to the largest V270 ‐ 270 L/min max. Higher flow‐rate meters are available to special order. The table at the end of this article assists in the selection of the best technology.

Sodium Hypochlorite Flowmeters ‐ Applications and Rates ‐ Pelton Wheel

Litre Meter started manufacturing the Pelton Wheel turbine in 1975. These usually had some stainless steel components together with a plastic rotor, elastomer seals and sapphire bearings. All plastic versions soon followed, including all Polypropylene, all PFA, all PVC and all PVDF. The other wetted parts are still sapphire with a suitable elastomer such as FKM or FFKM for the single O ring seal. The normal specification for Sodium Hypochlorite compatible Pelton Wheel flow meters is now PVC for the main body and cap with PVC or titanium internals, sapphire bearings, an FKM O‐ring and PFA rotor.

Pelton Wheel Flowmeter for Sodium Hypochlorite

The Pelton Wheel is an economical device with low pressure ratings and needs to have relatively steady state non‐pulsing flows.
The table at the end of this article assists in the selection of the best technology.

Compatible Materials

Due to the nature of Sodium Hypochlorite only a select group of tested materials is recommended by Litre Meter. We tailor our meters using three key materials, developed over 30 years of measuring Sodium Hypochlorite:

PVC, Hastelloy and titanium
The PVC design can be used up to 15 bar pressure maximum. Hastelloy (UNS N10276) up to 1035 bar. For the ultimate select titanium (UNS R50400) designed for 1380 bar (20,000psi, 20 ksi)

These material make up the body and the cap of the meter. The seals between the meter body and cap are normally FKM. Other seal materials include FFKM and PTFE. All seals within the meter are fully compatible with Sodium Hypochlorite.

Flow ranges and references

All Litre Meter manufactured flowmeters are custom calibrated across the customer specified minimum to maximum flow conditions and working viscosity. The minimum flow rates achievable are dependent on fluid viscosity. With sodium hypochlorite, in most normal concentrations, water is used as the calibration medium as this proves to be the best for accurate calibration representation. The table below assists in selecting which technology is preferred.
Normal engineering materials like 304 and 316 stainless steel, aluminium, brass and steel are unsuitable due to the aggressive nature of the free chlorine in the Sodium Hypochlorite. Plastics such as PVC and PTFE are suitable together with Hastelloy C and purer grades of Titanium.

Comparison table:
Table showing selection criteria for Sodium Hypochlorite meters in two different flow technologies.

Why should I measure Scale Inhibitor (and how)?

Money, money, money – or, as we now call it, Flow Assurance, coupled with a low flow meter

Allowing scale to build up on the inside of the pipeline may seem fairly inconsequential. However, when the amount of scale is considered, (and referencing the image) it is immediately obvious that the expensive crude will slow down and pumping costs will soar. Sign up for FlowSight, the Litre Meter newsletter.
Scaling reduces the area of a pipe if scale inhibitor is not used
Scaling reduces the area of a pipe if scale inhibitor is not used – Stock image
Chemists will analyse the crude oil as it comes out of the well, sometimes years before production starts. From geotechnical surveys other technicians will determine the rate of oil output through the anticipated life of the field.  With this data the chemist will recommend what the concentration of the scale inhibitor should be.  The pressure of the well will determine at which pressure the inhibitor needs to be injected at. Day to day the temperature will vary according to the seasons, the weather and location of the measurement.
The analysis of the crude, unrefined oil will tell the chemist whether the pipe will start to scale up as a result of pumping the oil through a pipe to the ship or refinery.  Certain chemicals are then formulated to optimise and negate the scale.  There will be compromises between concentration of the fluid, application flow rates and storage availability.  If the concentration can be increased so that the tanks only need filling up once per month then that is preferred to once per fortnight. Inevitably this means that the flow rate is lower, and probably, the viscosity increases. Measurement range will also vary through the life of the field. It may start slow, then plateau a few years later and then tail off as the field winds down.  Additionally to this, the consistency of the unrefined oil will probably change from start to finish.  All of these variables can lead to a range of viscosities and a range of flow rates.
In summary, selection of the meter philosophy and specification is critical to successful measurement of scale inhibitor and future condition of the oil pipeline.

The VFF rotary piston flowmeter has been used for many years to measure scale inhibitor at a variety of flow rates, pressures and viscosities.

VFF flowmeter for chemical injection service, with FlowPod display

What’s the best chemical injection flow meter? An expert explains:

Litre Meter VFF rotary piston positive displacement flowmeters have proven to be the foremost solution for chemical injection flow metering applications. They are able to handle the wide range of flows at pressures from a few bar up to 10,000 and 20,000 psi (690, 1,380 bar) and higher. The FlowPod instrument has been developed after feedback from many clients in the chemical injection arena, focussing on ease-of-use, compactness and functionality. Sign up for FlowSight, the Litre Meter newsletter.

In many chemical injection applications the VFF is the sole answer because of it’s unique capabilities at the ‘margins of measurement’. This might include super low flow rates and low viscosity or awkward chemical compatibility and material requirements. The standard range of VFF meters, available from 2015, was also designed in response to user feedback. It provides a number of bespoke chemical injection features that are no longer specials.  Since then, 80% of meters supplied have been from stock designs as opposed to 20% before.  This also means that drawings are immediately available including STEP files, lifting diagrams and parts lists.

Since 2013, as standard, all VFF meters have a URL given on the name plate and a QR code that links to a website with specific calibration certificates, manuals, hydrostatic test certificates and material certificates.

  • VFF positive displacement meters can measure accurately at any pressure and with a pulsing pump.  The measurement accuracy is unaffected by working pressure or change due to the unique construction.
  • VFF positive displacement meters can measure a range of chemicals at extreme low flows such as less than 100 ml per hour and at low or high viscosity.  Particle size limits are a generous 40 or 100 microns.
  • VFF positive displacement meters can measure a variety of chemicals requiring alternatives to 316L.  Titanium rotors are standard with titanium, super duplex and Hastelloy options for body and cap.
  • VFF positive displacement meters can be constructed using exotic materials and/or exotic material specifications. Litre Meter have developed their own material specification for 316L, duplex and super duplex. We have built meters from highly specified materials with extensive testing regimes to tight delivery times.

Call us now with your chemical injection metering requirements for probably the best flowmeter.  (it’s why LITRE METER RECEIVES A QUEEN’S AWARD FOR ENTERPRISE)

VFF Flowmeter Sizes and Connections.

What’s the best chemical injection flow meter?

Litre Meter VFF rotary piston positive displacement flowmeters have proven to be the foremost solution for chemical injection flow metering applications. They are able to handle the wide range of flows at pressures from a few bar up to 10,000 and 20,000 psi (690, 1,380 bar) and higher. The FlowPod instrument has been developed after feedback from many clients in the chemical injection arena, focussing on ease-of-use, compactness and functionality. Sign up for FlowSight, the Litre Meter newsletter.

In many chemical injection applications the VFF is the sole answer because of it’s unique capabilities at the ‘margins of measurement’. This might include super low flow rates and low viscosity or awkward chemical compatibility and material requirements. The standard range of VFF meters, available from 2015, was also designed in response to user feedback. It provides a number of bespoke chemical injection features that are no longer specials.  Since then, 80% of meters supplied have been from stock designs as opposed to 20% before.  This also means that drawings are immediately available including STEP files, lifting diagrams and parts lists.

Since 2013, as standard, all VFF meters have a URL given on the name plate and a QR code that links to a website with specific calibration certificates, manuals, hydrostatic test certificates and material certificates.

  • VFF positive displacement meters can measure accurately at any pressure and with a pulsing pump.  The measurement accuracy is unaffected by working pressure or change due to the unique construction.
  • VFF positive displacement meters can measure a range of chemicals at extreme low flows such as less than 100 ml per hour and at low or high viscosity.  Particle size limits are a generous 40 or 100 microns.
  • VFF positive displacement meters can measure a variety of chemicals requiring alternatives to 316L.  Titanium rotors are standard with titanium, super duplex and Hastelloy options for body and cap.
  • VFF positive displacement meters can be constructed using exotic materials and/or exotic material specifications. Litre Meter have developed their own material specification for 316L, duplex and super duplex. We have built meters from highly specified materials with extensive testing regimes to tight delivery times.

Call us now with your chemical injection metering requirements for probably the best flowmeter.  (it’s why LITRE METER RECEIVES A QUEEN’S AWARD FOR ENTERPRISE)

VFF Flowmeter Sizes and Connections.

Electronic documentation – leading the way

Litre Meter now provides all documentation electronically for it’s manufactured flowmeters.  That’s not just a manual emailed to the client, either.  Each meter has a product label and includes a QR code and URL. At the website location there’s a minimum of a calibration certificate, quick start instructions and a full Installation and Operation Manual (IOM). Most will also have material certificates, hydrostatic test certificates, wiring diagrams and a function test cert. Sign up for FlowSight, the Litre Meter newsletter.

The product label is comprehensive, providing all calibration data.  The URL provides everything else the installation engineer might need. Using a smart phone and scanning the QR code is even more convenient.

Charles Wemyss, CEO of Litre Meter, says:”If a client needs any information emailed we just send the link. For larger projects with a number of flowmeters and larger documentation packages we include a single zip file for ease of downloading.  We’ve been providing this as part of our service since 2013 and our customers love it! This is a project dear to our hearts that cuts waste right down and provides our clients with a very quick and easy access point.  As far as we know, there is no other instrumentation company providing this level of data direct to their clients.”.
Litre Meter QR code allows remote access to documentation

KEM Küppers Subsea flowmeter solutions

Litre Meter are now the exclusive distributors for KEM Küppers. In addition to their standard ranges of positive displacement and turbine flowmeters KEM offer a customisation service that encompasses the necessary modifications and approvals for subsea service. Both the ZHM gear meter and HM turbine meter have versions that are designed to rigorous subsea specifications. The subsea versions have encapsulated electronics, a welded stainless steel cover and an FEA designed housing that remains stable at high external pressures. All of these are manufactured by Litre Meter’s sister company KEM Küppers in Germany. Sign up for FlowSight, the Litre Meter newsletter.

Two Subsea Applications:

Production – Blow Out Preventers (BOPs) are large subsea control valves used to prevent uncontrolled release of pressure or flow of fluid during well drilling operations or production. The hydraulic valve can be remotely controlled to close or open to avoid a “blow out”, and are typically installed multiple times in stacks as a precaution. Maintenance of BOPs and regularly testing is a very high priority for both the oil company and drilling rigs. Subsea turbine flow meters are used on the hydraulic fluid to monitor the valves to ensure that they are functioning correctly when needed.

ZHM: Positive displacement gear meter with wide flow range. Image shows subsea cover and connector.

Subsea chemical injection – As oil is pumped from the subsea well, many chemicals and additives are injected to ensure maximum productivity. In many cases, oil companies install subsea flow meters to measure these chemicals at the point of entry, which is often far below the surface, instead of topside where the liquid has to travel a great distance before entering the flow stream. Often this is more cost effective. Subsea Positive Displacement (PD) flow meters are used to inject additives such as mono ethylene glycol (MEG), methanol, and low-dose inhibitors (LDIs).

HM: Axial turbine flowmeter, redesigned for subsea duty, with subsea electrical connectors.

Call Litre Meter now for further information. 01296 670200. www.litremeter.com

What is linearisation – what is it and why do I need it?

Linearisation is a process that enhances the accuracy of any repeatable flowmeter. Sign up for FlowSight, the Litre Meter newsletter.

This article will show the amount of accuracy increase that can be expected from optimising linearisation points in terms of number and position.

A standard calibration of a VFF flowmeter will involve 10 calibration points. These are always spread out along the customer’s operating flow range. They will be distributed in favour of lower flow rates – where changes in raw meter accuracy are higher.

Below is an example of a flowmeter calibration curve. The results of a calibration are a table of flow rates and the corresponding pulses per litre.  In an ideal world, there would be a hundred or a thousand such points so that the complete curve could be plotted and for any given flow rate the pulses per litre would be known. In practice, there are usually 10 to 20, distributed as shown.

A plot of flow rate against frequency would be an apparently straight line relationship.  The angle of the straight line would be the ‘meter factor’ or the average number of pulses per litre.

Flowmeter linearisation. Flow rate versus frequency.

Flowmeter linearisation. Flow rate versus frequency.

To make this more visual, it’s common to plot the flow rate against the ‘pulses per litre’. This emphasises the changes as the flow rate increases.

Flowmeter meter factor or 'k' factor plotted against flow rate.
Flowmeter meter factor or ‘k’ factor plotted against flow rate.

Better still is a plot of flow rate against accuracy using the ‘meter factor’ as a zero.  The biggest positive excursion defines the positive error and the biggest negative excursion is the negative error.

Flowmeter linearity expressed as percentage error versus flow rate
Flowmeter linearity expressed as percentage error versus flow rate.

If the flowmeter is repeatable then we can use a technique called linearization.  In other words, if the curve (i.e. the relationship between flow rate and pulses per litre) is the same the next time around, then the flow rate can be calculated from the frequency output using the specific pulses per litre value rather than an average pulses per litre value.  If the flow rate is identical to one of the original calibration points there is no adjustment. At other flow rates a calculation is required.  In between the points most linearization systems use simple linear interpolation. For example, if the flow rate is halfway between two original calibration points then an average of the pulses per litre for those two points is used.

The error is represented here by the length of the red arrow.

Linearisation is normally linear interpolation between two points. The difference between the brown linear interpolation and the blue real value is the subsequent error.
Linearisation is normally linear interpolation between two points. The difference between the (brown) linear interpolation and the (blue) real value is the subsequent error.

Now the measurement error is no longer compared to a single meter factor from min to max but a linearity curve built into the meter.

By carefully selecting the calibration flow rates along the range the remaining error can be minimised.  In the example below, the actual curve (in blue) is shown plus the linear approximation (in brown).

The meter character and the linear interpolation between linearisation points for the whole range of the meter
The meter character and the linear interpolation between linearisation points for the whole range of the meter.

Magnified in scale:Here is how this linearization improves the accuracy, on the same scale:

Results of the linearisation.
Results of the linearisation.

Magnified in scale:

The result of linearisation. Now between +0.19% and -0.28%.
The result of linearisation. Now between +0.19% and -0.28%.

And here is the result, if there are 4 calibration points at the lowest flow rates rather than 2.

Concentrating the calibration and linearisation points at low flows, in this example, has a further impressive improvement to overall linearity.
Concentrating the calibration and linearisation points at low flows, in this example, has a further impressive improvement to overall linearity.

As a result of linearization, the overall error has been reduced from max error: 1.19%, min error: -3.98% to max error: +0.19%, min error: -0.28% representing an 11x improvement.  Selecting the calibration points carefully improves this further.  Every calibration point has a cost so there are diminishing returns. If the repeatability is +/- 0.25% then 10 points overall are normally enough.

If enough calibration time is available and the repeatability of the system is considerable then more points can be selected for the linearisation table.  In this extension of the example above 21 points are used rather than just 10.  Arranged carefully throughout the flow range, the net effect is to reduce the max/min to 0.08%, a 64x improvement over the non-linearised version.  If the repeatability of the system was ±0.1% then no more points are required.The flowmeter response (blue) is almost perfectly matched by 21 carefully selected calibration points (brown).

The flowmeter response (blue) is almost perfectly matched by 21 carefully selected calibration points (brown).
The flowmeter response (blue) is almost perfectly matched by 21 carefully selected calibration points (brown).
The final analysis. Total non-linearity reduced from 5.17% to 0.08%.
The final analysis. Total non-linearity reduced from 5.17% to 0.08%.

This article shows that linearisation with a flowmeter instrument can significantly improve the linearity of the flowmeter system.  In this example, if the meter is repeatable, then 6 to 60 times improvements are possible.

Next article: Is there good and bad linearisation?

Sign up for FlowSight, the Litre Meter newsletter.

What is linearisation – what is it and why do I need it? An expert explains:

Linearisation is a process that enhances the accuracy of any repeatable flowmeter. Sign up for FlowSight, the Litre Meter newsletter.

This article will show the amount of accuracy increase that can be expected from optimising linearisation points in terms of number and position.

A standard calibration of a VFF flowmeter will involve 10 calibration points. These are always spread out along the customer’s operating flow range. They will be distributed in favour of lower flow rates – where changes in raw meter accuracy are higher.

Below is an example of a flowmeter calibration curve. The results of a calibration are a table of flow rates and the corresponding pulses per litre.  In an ideal world, there would be a hundred or a thousand such points so that the complete curve could be plotted and for any given flow rate the pulses per litre would be known. In practice, there are usually 10 to 20, distributed as shown.

A plot of flow rate against frequency would be an apparently straight line relationship.  The angle of the straight line would be the ‘meter factor’ or the average number of pulses per litre.

Flowmeter linearisation. Flow rate versus frequency.

Flowmeter linearisation. Flow rate versus frequency.

To make this more visual, it’s common to plot the flow rate against the ‘pulses per litre’. This emphasises the changes as the flow rate increases.

Flowmeter meter factor or 'k' factor plotted against flow rate.
Flowmeter meter factor or ‘k’ factor plotted against flow rate.

Better still is a plot of flow rate against accuracy using the ‘meter factor’ as a zero.  The biggest positive excursion defines the positive error and the biggest negative excursion is the negative error.

Flowmeter linearity expressed as percentage error versus flow rate
Flowmeter linearity expressed as percentage error versus flow rate.

If the flowmeter is repeatable then we can use a technique called linearization.  In other words, if the curve (i.e. the relationship between flow rate and pulses per litre) is the same the next time around, then the flow rate can be calculated from the frequency output using the specific pulses per litre value rather than an average pulses per litre value.  If the flow rate is identical to one of the original calibration points there is no adjustment. At other flow rates a calculation is required.  In between the points most linearization systems use simple linear interpolation. For example, if the flow rate is halfway between two original calibration points then an average of the pulses per litre for those two points is used.

The error is represented here by the length of the red arrow.

Linearisation is normally linear interpolation between two points. The difference between the brown linear interpolation and the blue real value is the subsequent error.
Linearisation is normally linear interpolation between two points. The difference between the (brown) linear interpolation and the (blue) real value is the subsequent error.

Now the measurement error is no longer compared to a single meter factor from min to max but a linearity curve built into the meter.

By carefully selecting the calibration flow rates along the range the remaining error can be minimised.  In the example below, the actual curve (in blue) is shown plus the linear approximation (in brown).

The meter character and the linear interpolation between linearisation points for the whole range of the meter
The meter character and the linear interpolation between linearisation points for the whole range of the meter.

Magnified in scale:Here is how this linearization improves the accuracy, on the same scale:

Results of the linearisation.
Results of the linearisation.

Magnified in scale:

The result of linearisation. Now between +0.19% and -0.28%.
The result of linearisation. Now between +0.19% and -0.28%.

And here is the result, if there are 4 calibration points at the lowest flow rates rather than 2.

Concentrating the calibration and linearisation points at low flows, in this example, has a further impressive improvement to overall linearity.
Concentrating the calibration and linearisation points at low flows, in this example, has a further impressive improvement to overall linearity.

As a result of linearization, the overall error has been reduced from max error: 1.19%, min error: -3.98% to max error: +0.19%, min error: -0.28% representing an 11x improvement.  Selecting the calibration points carefully improves this further.  Every calibration point has a cost so there are diminishing returns. If the repeatability is +/- 0.25% then 10 points overall are normally enough.

If enough calibration time is available and the repeatability of the system is considerable then more points can be selected for the linearisation table.  In this extension of the example above 21 points are used rather than just 10.  Arranged carefully throughout the flow range, the net effect is to reduce the max/min to 0.08%, a 64x improvement over the non-linearised version.  If the repeatability of the system was ±0.1% then no more points are required.The flowmeter response (blue) is almost perfectly matched by 21 carefully selected calibration points (brown).

The flowmeter response (blue) is almost perfectly matched by 21 carefully selected calibration points (brown).
The flowmeter response (blue) is almost perfectly matched by 21 carefully selected calibration points (brown).
The final analysis. Total non-linearity reduced from 5.17% to 0.08%.
The final analysis. Total non-linearity reduced from 5.17% to 0.08%.

This article shows that linearisation with a flowmeter instrument can significantly improve the linearity of the flowmeter system.  In this example, if the meter is repeatable, then 6 to 60 times improvements are possible.

Next article: Is there good and bad linearisation?

Sign up for FlowSight, the Litre Meter newsletter.

VFF FilterPro filter protects VFF meters from contamination

Litre Meter introduces the VFF FilterPro Filter that maximizes the efficiency of its flow meters by eliminating contaminants that cause reduced flow, damage to internal construction as well as a blockage.  As 96% of flow meter failures are associated with contamination issues, the FilterPro protects flow measurement instrumentation, assuring optimal flow in liquid injection, batch processing, and lubrication systems. Sign up for FlowSight, the Litre Meter newsletter.

VFF FilterPro - a filter to match your VFF Flowmeter
VFF FilterPro – a filter to match your VFF Flowmeter

Featuring a four-layer wire woven mesh filtration design, the FilterPro uses a proven surface filtration principle that filters elements from 10 to 100 microns (depending upon unit option) by trapping particulates between its layers.  Available in three key filter sizes, the FilterPro pairs perfectly with the company’s positive displacement, rotary piston, and turbine flow meters with connection sizes from ¼” up to 9/16” in multiple thread types.   Offered in 316 stainless steel or exotic materials, the FilterPro is available in the same materials as VFF flow measurement instrumentation to avoid compatibility and performance variances.

Units are suitable for use in low and high viscosity liquids at pressures up to 20,000 psi (1,380 bar) and can withstand a pressure drop of 870 psi (60 bar) with a burst pressure drop of 2,175 psi (150 bar).  Simple to install, the FilterPro is easily cleaned by unscrewing 8 bolts and replacing the filter insert.  The company is currently developing larger filters to accommodate larger meters while incorporating a filter maintenance indicator and greater resistance to burst pressure. Sign up for FlowSight, the Litre Meter newsletter.

VFF FilterPro pressure drops for viscosity and flow rate values - 30 micron
VFF FilterPro pressure drops for viscosity and flow rate values – 30 micron
Exploded view of VFF FilterPro with annotation
Exploded view of VFF FilterPro showing simplicity of design and disassembly
VFF FilterPro with filter cartridges
VFF FilterPro with filter cartridges, available in 10, 30 and 100 micron sizes
VFF FilterPro Dimensions - threaded body
VFF FilterPro Dimensions – threaded body – NPT or Autoclave Medium Pressure. Other connections on request.
VFF FilterPro typical materials and pressure ratings
VFF FilterPro typical materials and pressure ratings

 

VFF FilterPro typical connections and pressure ratings
VFF FilterPro typical connections and pressure ratings

20k meters – brochure available

Litre Meter have been making meters for higher pressures for over 3 decades. Our first 1,380bar unit was shipped in 1997.  We’ve now produced a brochure to cover these ratings.

Download the 20k VFF datasheet
20,000 psi rated VFF flowmeters – brochure

Litre Meter have been manufacturing flowmeters since 1975. We’ve always concentrated on the harder margins of metering typically at low flows and/or at high pressure. The VFF range has many uses in the oil and gas industry and meets the high specifications required. Outside of oil and gas we have manufactured these to 2,500 bar. We have recently noticed a trend towards 20,000 psi ratings and this brochure is in response to that.

Since 1997 Litre Meter has made numerous VFF meters for 1,380 bar in Oil and Gas applications and a reference list is provided at the end of this article.
The same design can be used on 22.5ksi (1,550 bar) with little modification.
The breakthrough in our design philosophy came in 2005 when we separated the measurement of the fluid from the pressure containment. We designed a measurement chamber that floats in the pressure vessel. This ensures accurate, pressure independent flow metering from 10 psi to 20,000 psi. The Pressure Balance Chamber is explained below.

Key Features

  • Rotary Piston/ Oscillating Piston type flow meter with a single moving part provides robust and low maintenance technology.
  • Suitable for low & high viscosity liquids at pressure ratings up to 4,000 bar (60,000 psi). 20,000 psi designs as standard.
  • Available materials of construction: 316L (UNS S31603), Duplex F51(UNS S31803), Super Duplex F53(UNS S32750)/F55(UNS S32760), 6Mo F44(UNS S31254), Hastelloy (UNS N10276) & Titanium (UNS R56400).
  • Connections: Autoclave, Grayloc Hubs, Galperti Hubs, Techlok hubs. More on request.
  • Communications: 4‐20mA HART, Pulse, MODBUS, Foundation Fieldbus, dependent on electronics and certification requirements.
  • Compact
  • Very Low Flow Measurement
  • Tolerant of particulate up to 100+ microns
  • Low pressure drop (<0.1 bar typical)

20K Flowmeters ‐ Applications and Rates

The VFF has successfully metered fluids such as oils, hydraulic fluids, corrosion / wax / asphaltene / demulsifier / pour point depressant (PPDs) /scale / hydrate inhibitors, biocides, oxygen scavengers, etc. for over 30 years. Meter bodies are produced in a variety of high grade materials which offer good chemical and environmental resistance.
Applications for flow‐rates as low 0.00013 litres/min (0.19 litres/day) have been metered within the offshore oil industry. The VFF flow meter provides exceptional rangeability with potential turndowns of up to 3000:1, dependent on operating viscosity.
The meters range in size from the smallest standard stock size, LF03 ‐ 18 L/Hr max, to the largest V270 ‐ 270 L/min max. Higher flow‐rate meters are available to special order.
An extensive range of meter designs and materials offers pressure ratings to 20,000 psi (1,380 bar). Higher pressure rating designs are manufactured up to 4,000 bar (60,000 psi). 20,000 psi designs available, as standard, up to HF60 and special designs can measure higher flow rates.

20K Flowmeters ‐ Meter Sizes

The VFF meter is not just one size, one specification. It’s a comprehensive range of carefully engineered devices to meet today’s standards in the most demanding oil & gas arenas. It’s truly a Versatile Fluids Flowmeter.

In the illustration below the smallest meter is typically housing an LF05 or LF15 rotor and chamber with FlowPod instrument and Autoclave Engineers MP connections.

The middle unit is a medium size meter, say, VFF4 with hub connections and FlowPod display.

The right‐hand meter also has hubbed connection sizes, FlowPod display but is larger to accommodates the HF60 rotor and chamber.

VFF Flowmeter Sizes and Connections.
VFF Flowmeter Sizes and Connections.

Pressure Balance Chamber

What Is a Pressure Balance Chamber?
Extensive testing by Litre Meter in 2005 proved that leaks occur over the top of the rotor at higher pressures. This is due to minute distortions of the cap. For example, at 700 bar the cap moves by just 0.02mm in the centre. Increasing the bulk of the cap still produces this movement. The effect on meter performance was the creation of a leak path for fluid that avoided the positive displacement of the rotor. This was equivalent to about a 3% inaccuracy at 700 bar. As a result, of this Litre Meter designed a pressure balance chamber for its VFF flowmeters so it could operate at extreme pressure and at low flow rates. The pressure balance chamber acts as a barrier, protecting the internal measurement components of the instrument from the high pressure conditions, preventing them from expanding and contracting under the immense pressure. NO DISTORTION MEANS ACCURATE MEASUREMENT AT ANY PRESSURE. All VFFs over 414 bar are fitted with this technology. It is identified by the letters PBC in the calibration certificate.
Key Benefits:

  • No distortion of the chamber at higher pressures.
  • Enables selection of optimal materials for the chamber to match the rotor i.e. PVD coated stainless steel or titanium.
  • Enables selection of optimal materials for the pressure vessel.
  • Enables construction of a duplex bodied flowmeter.
  • Swappable PBC for simplified sparing.

Flow ranges and references

All VFF flowmeters are custom calibrated across the customer specified min – max flow conditions and working viscosity. The minimum flow rates achievable are dependent on fluid viscosity. To see the achievable calibration ranges for each meter size please consult the table below. We can offer meters that range from 0.005 L/hr to 3,600 L/hr at 20K pressures to best suit your applications and with exceptional turndowns.

20K flow ranges

Areas of key significance:

  • Extended experience in measuring 20,000 psi in Oil & Gas applications.
  • World leaders in low flow and high pressure measurement.
  • High or low viscosity fluids flow measurement.
  • The Chemical Injection Specialists.
20,000 psi reference list
20,000 psi reference list VFF meters

Future developments

Litre Meter have already provided meters for 2,500bar. Offshore models at 22.5k & 25k are designed and 30k, 40k and 50k will be produced.
Litre Meter continues to innovate in the field of flow measurement. Recent successes include the LF05 and LF03 size meters, a new sensor, the FlowPod instrument and the FlowLabPro calibrator series. In the near term, expect to see lower flow capabilities, more calibrators and a low flow meter for any liquid type.

Offshore Corrosion Inhibitor Measurement at 20,000psi

APPLICATION: Various chemicals are injected into a deep water well to prevent corrosion, paraffins, hydrates, and scale. The flow rates for the injection are generally very low and need to be metered precisely to prevent under or over-dosing a well.

PRODUCTS SUPPLIED: • VFF series LF03, LF05, and LF15 • HM turbines HM-007 and HM-009/TC-AC/S-EX

CHALLENGE: As oil exploration goes into deeper and deeper water and deeper reservoirs, new challenges arise that put current technology to the test. The newest development is reservoirs that are reaching pressures of up to 20,000 psi. The chemicals need to be injected at a pressure that will overcome the force of the oil flowing up the umbilical.

SOLUTION: By utilizing different technologies available through the TASI Flow portfolio, we were able to offer a solution for this unique chemical injection challenge.
Positive displacement meters from Litre Meter were used for their ability to measure ultra-low flows and their flexible materials of construction that allows for high tensile strength steels exceeding the 20,000 psi pressure requirement. For the higher flow methanol and LDHI applications, the high pressure HM turbine line from AW was used for their ability to measure very non-lubricating fluids while also achieving the desired pressures.
The hazardous area location of these meters also require that all electrical components be hazardous area certified. Because of the close cooperation in development between AW and Litre Meter, as well as all other TASI Flow brands, we were able to offer a single type of user interface for all the meters. Using Litre Meter’s FlowPod transmitter in conjunction with the AW HUB-40EX pickup added a uniformity to the installation of all the meters on the chemical skid.

Corrosion Inhibitor measured at 20,000 psi 1380bar
Corrosion Inhibitor measured at 20,000 psi 1380bar

RESULTS: This is simply one of the first projects heading to locations with reservoirs up to 20,000 psi. In the near future equipment manufacturers in this segment of the market are going to need to produce technology that can keep up with industry needs. TASI Flow’s continuing innovations and ability to customize will allow them to keep pace with the constant change in the O&G production environment. Sign up for FlowSight, the Litre Meter newsletter.

Fuel and fuel additive test system uses Tricor for final testing of Formula 1 gasoline pumps

APPLICATION: Fuel and fuel additives test system for final testing of gasoline pumps at Parker Hannifin Manufacturing Germany GmbH & Co. KG in Mainz-Kastel. The pumps are used by Formula 1 racing teams. Every single gasoline pump is tested and qualified on the test system under completely different operating parameters before they are delivered to the racing customers.

CHALLENGE: A test system of high technical complexity was being designed and modelled for unlimited final testing of gasoline pumps for Formula 1 racing customers. To meet the very high demands for quality, the test must cover the entire performance spectrum and provide the optimum testing conditions for the final test. In the area of flow measurement, the task was to specify a highly accurate sensor for the most varied operating parameters. The flow conditions comprised a large spread in temperature and process pressure. This resulted in a change in the viscosity of the fuel. In the first design, turbine flow meters and TRICOR Coriolis mass flow meters were considered. The solution with turbine flow meters required a cascading of several devices to cover the required flow measurement range. Furthermore, different calibration curves needed to be used in order to meet the accuracy requirements.

TCM 0650-FA-HGSS-CSDS Tricor Coriolis for fuel measurement
TCM 0650-FA-HGSS-CSDS Tricor Coriolis for fuel measurement

SOLUTION: TRICOR Coriolis mass flow meters, by contrast, provide multiple technical advantages for this test bed. Flow meters using the Coriolis principle are significantly more accurate, faster and are almost completely independent from the medium properties like viscosity, temperature and pressure – in contrast to some other flow meters. The TCM 0650 covers the entire testing measurement range. With the TRICOR Coriolis solution, Parker Hannifin can cover the required temperature and process pressure range on the fuel test bed with one device. There are no restrictions in regards to fluid, viscosity or accuracy of measurement. Additional components for a cascading measurement (such as needed with the turbine flow meter option) and the associated added expense are eliminated.

CUSTOMER ADVANTAGE: All requirements are met by the broad measurement range of a single TCM 0650. It reduces not only the purchasing costs but also the costs for having replacement devices. Using analogue output signals and modbus TRU interfaces, mass flow, volume flow, temperature and medium density can be read out at the same time on the local display – remote optional. The TCM 0650 is the optimal solution for Parker Hannifin in order to master this challenging measuring task.

 

http://tricorflow.com/wp-content/uploads/2016/02/TRICOR_AS_fuel-fuel_additive_test_system_F1_gasoline-pumps.pdf

Exclusive distributors of KEM Kuppers flowmeters

Litre Meter are now the exclusive UK distributors of the KEM Küppers range of flowmeters.  These include the ZHM, SRZ positive displacement, HM turbine and the Tricor coriolis series. Sign up for FlowSight, the Litre Meter newsletter.

KEM ZHM01/3 gear meter
KEM ZHM01/3 gear meter

ZHM: Positive displacement gear meter with wide range and in a variety of materials including aluminium and 316 stainless steel.

HM series turbine meters
HM series turbine meters

HM: Axial turbine flowmeter, also in range of materials, from 0.03 to 25,000 litres per minute and up to 350°C.

SRZ helical screw positive displacement flowmeter
SRZ helical screw positive displacement flowmeter

SRZ: Helical screw positive displacement flowmeter combining exceptional accuracy and viscosity rangeability.  Flows from 0.01 to 400 litres per minute. Low pressure drop.

Tricor coriolis mass flowmeters
Tricor coriolis mass flowmeters

Tricor: Coriolis mass flow meter for gases and liquids. Smallest size available in very high pressure rating (1550bar). Range measures from 3 to 230,000 kg per hour, and higher.

All of these units are manufactured in Germany by Litre Meter’s sister company, KEM Kueppers GmbH. Sign up for FlowSight, the Litre Meter newsletter.

 

 

Chemical Manufacturing – Chlorine Gas – Coriolis application

APPLICATION: A bayonet-style heat exchanger is used by this customer to heat and vaporise dry liquid Chlorine, to supply multiple reactors at various flow rates with Chlorine gas, at 54°C (130°F) and 180 psig. Pure liquid Chlorine is fed to the vaporizer from a pressurized railcar. The heat source was low pressure steam. The existing system did not control the liquid level in the vaporizer nor the flow of the liquid Cl2, and the vapourizer’s liquid level was limited by equilibrium.

TRICOR PRODUCT SUPPLIED: TCM-28K Hastelloy Coriolis Mass Flow Meter with Integral Transmitter

Using Tricor Coriolis meter for the transfer of chlorine. Hastelloy selected.
Using Tricor Coriolis meter for the transfer of chlorine. Hastelloy selected.

CHALLENGE: Chlorine has a high coefficient of thermal expansion. Process upsets or momentary shutdowns sometimes resulted in excessive liquid levels, which rapidly led to undesired pressure excursions. There were also cases of low liquid levels, which led to super-heating of the gas. This problem was compounded by the over-sized tube bundle in the vaporiser.

SOLUTION: Since a very small amount of liquid CL2 can lead to serious swings in level, and therefore over-pressure excursions, a highly accurate and repeatable flow meter was required. The customer chose the TRICOR TCM-28K Hastelloy C-22 flow meter. The C-22 alloy features excellent corrosion resistance to Chlorine, and has proven to be superior to C276 for these applications.

RESULT: The new system uses re-circulating hot water as a heat source, rather than steam, and the CL2 liquid level is now controlled via a cascade master and a mass flow control loop.

Tricor coriolis meter selected in Hastelloy for Chlorine measurement
Tricor coriolis meter selected in Hastelloy for Chlorine measurement

 

 

 

 

 

 

 

 

see the full brochure:

http://tricorflow.com/wp-content/uploads/2015/04/TRICOR_AS_Chemical_Manufacturing_Chlorine.pdf

 

Tricor Coriolis – available from Litre Meter

Petrochemical Processing – Oil Additive Blending – Tricor Coriolis

APPLICATION DESCRIPTION: This lubricant manufacturer now uses two TRICOR Coriolis meters: one measures the individual petrochemical products as they are offloaded into their tank farm, and the second is for batch control as they create products using components from various tanks. The Coriolis meter for batching is used with a Precision Digital Batch Controller and a pneumatic control valve for precise batching.

TRICOR PRODUCT SUPPLIED: TCM-65K Coriolis Mass Flow Meter with Integral Transmitter

CHALLENGE: This customer used multiple hydrocarbon components to create their products, and some components are measured using a manual weight scale. The display was hard to read and the weight scale was unreliable. Additionally, hydrocarbon components were not being measured upon delivery by the customer.

tricor-blending
The Tricor Coriolis installed on the hydrocarbon line

SOLUTION: One 2-inch Coriolis flow meter was placed in the receiving pipeline for measurement of the individual components as they are off-loaded from delivery trucks to the individual storage tanks which provided accurate measurement and billing. Also, by using the batch controller, control valve and Coriolis meter for the batching process, the customer can now dial in the desired amount of individual components and then walk away. These flow meters were also integrated into a local display, a Precision Digital Consolidator which displays values of tank levels and flow rate.

Tricor Coriolis used for blending
Tricor Coriolis used for blending

RESULT: The new batching system is set to control the flow rate, totalize the flow, and shut off the flow when the setpoint is reached. The customer is pleased with the accuracy achieved.

http://tricorflow.com/wp-content/uploads/2015/04/TRICOR_AS_Petrochemical_Additive_Blending.pdf

Available from Litre Meter.

Dimethylformamide (DMF) measurement with Tricor

TRICOR_Chemical_Manufact._DMF_EN_spotlight_160705_E002

DMF (Dimethylformamide, N,N-Dimethylmethanamide, (CH3)2NC(O)H) is a clear liquid organic solvent used in a number of industrial processes, particularly in the manufacture of polyurethane products, pesticides, electrical equipment, pharmaceuticals, and synthetic leathers and fibres. The Tricor coriolis meter proved itself on this technically challenging application using standard equipment.

 

Tricor coriolis mass flowmeters used in the flow measurement of DMF
Tricor coriolis mass flowmeters used in the flow measurement of DMF

TECHNICAL DATA:

Medium: DMF

Pressure: >4 bar

Density: 995 kg/m3

Viscosity: 2 cSt

Flow range: up to 20,000 kg/h / 50,000 kg/h for loading and unloading

Flow range: up to 12,000 kg/h / 25,000 kg/h for product supply for a PU coating agent into the reactor.

 

TRICOR PRODUCT SUPPLIED:

TCM 028K Coriolis Mass Flow Meters (28,000 kg/hr max)

TCM 065K Coriolis Mass Flow Meters (65,000 kg/hr max)

TRICOR_Chemical_Manufact._DMF_EN_spotlight_160705_E002 Brochure

https://www.litremeter.com/Coriolis/Tricor_Flowmeters.php

Coriolis
Tricor coriolis mass flowmeters used in the flow measurement of DMF

Expert advice on flowmeters and calibration

Charles Wemyss lists 10 reasons why you should – and should not – calibrate your flowmeter

We use the word flowmeter to describe a device that measures the flow of a fluid. Mostly we’re considering gases or liquids in a closed pipe or conduit and we need either the instantaneous flow rate or the total amount of fluid that has passed. There are many varieties of techniques dependent on the fluid being measured and dependent on the flow rate, pressure, viscosity and more. The flowmeters range from miniature positive displacement devices to large electromagnetic or ultrasonic units used for pipes over 3m diameter. The way we garner confidence in the displayed value is through calibration.

Most flowmeters are supplied by the manufacturer with a ‘laboratory’ calibration. In other words, they have been tested in close to ideal conditions. Depending on the meter type, once installed in your process, that original calibration may be valid – or it may not be.

Litre Meter’s latest rig FlowLabPro is designed for calibrating ultra-low flowmeters

There are a number of key reasons why it should be calibrated:

* To reflect the new, current conditions

* Because some component has a wear factor

* There is an accumulation of dirt or setting product, affecting the sensor

* Because the calibration frequency states it has to be

* Because the results don’t feel right compared to the rest of the process

* The process is producing poor quality product yet the flowmeter seems stable.

The best calibration is that which is performed in situ. Many of the variables are tuned out. The fluid is the same, as is the installation attitude, straight lengths, etc. That’s the precise reason why you should re-calibrate; it gives you that confidence in the device. If in situ is not possible, for example, when the fluid is hazardous or at high pressure then it has to be uninstalled and calibrated elsewhere.

Why shouldn’t it be calibrated?

Clean versus dirty is the first argument for not calibrating your flowmeter. If it comes out of the line dirty and is sent away for calibration then you’d normally expect to ship it clean. The test lab calibrates it in the clean state. However, as soon as you re-install it the process might be depositing dirt back on it. It has been calibrated for a perfect installation and is almost immediately imperfect.  In this scenario, calibration is pointless.

Next, it’s hard to compare installation to installation. All calibration laboratories pride themselves on making adequate provisions for calibration, especially good installation practice. If they’re testing a turbine meter, for example, then they should have a long length of correctly sized piping before the meter – and a length after, too. This eliminates swirl, if it’s long enough, to generate a flat flow profile and present optimum conditions to the meter. Most labs have this setup for horizontal installation – so if you have a vertical install, then watch out. Likewise, if you don’t have a long length of correctly sized pipe, or perhaps a connector that necks the diameter down a few percent, then don’t bother. The results they give you will be meaningless.

The Litre Meter low flow rig FlowLabPro delivers automatic calibration of flowmeters and instrumentation within a flow range of 0.0006 to 200 l/hr to an accuracy of ±0.2%

Next you should ask whether it is the right fluid. Unless your process is running clean water or, maybe a calibration fluid, then your average lab will not be able to calibrate with the same fluid. For some flowmeter types this may not be important. For example, if you fluid is a weak acid with a viscosity of 1.2cP and the meter is an electromag, then the calibration with water will be perfectly valid. Contrarily, if you have 10cP process fluid and it’s a turbine meter then it could be very important that the test fluid is in the 9 to 11cP range to adequately represent the effect of viscosity on meter performance at lower flows.

Traceability is next on the list. If you have been able to clear the hurdles above then it’s important you pick a lab that has the right traceability for you. If your process demands an indication of flow within +/- 4% then there’s little point on getting a UKAS-accredited laboratory with an uncertainty level of 0.22%.

We’re regularly asked ‘how often should it be calibrated?’ Recalibration periods of flowmeters are based on industry standards. In industrial applications, depending on the industry, periods of six to 12 months are recommended. We advise the user to seek out data relating to the process, other components within the process and the usage of the meter. If the measurement is critical then the recalibration should be more frequent than a non-critical, rarely used device. In the absence of any other data we advise an annual check and to vary the future calibration periods depending on results.

If it has remained unused then no recalibration may be necessary, depending on the meter type. It is wise to check that no fluid has settled in the meter that might alter the way the meter works or even cause corrosion. In the event of any doubt then the manufacturer is always your best source of advice.

{originally published in International Process Engineer in May 2016, www.engineerlive.com}

What is a flow meter and how does it work?

Flow gauge, flow indicator, liquid meter, flow meter – they’re all the same thing; depending on the industry they may have different names, but their function remains the same: to measure flow.

In the simplest of terms, a flow meter is a device which is used to measure the quantity and/or flow rate of a gas or liquid as it moves through a pipe. Some flow meters measure the amount of fluid that passes through the pipe in a given time, while others measure the total amount of fluid or gas that has passed through the flow meter. Sign up for FlowSight, the Litre Meter newsletter.

 

How do flow meters work?

Flow meters consist of three parts: a primary device, a transducer, and a transmitter. As the fluid passes through the primary device, the transducer senses it; the raw signal from the transducer is then sent to the transmitter and turned into a usable flow signal.

Mathematically speaking, a flow meter typically uses the following equations:

  • Q = A · v – Where the volume of fluid passing through a flow meter is equal to the cross-sectional area of the pipe (A) multiplied by the average velocity of the fluid (v).
  • W = r · Q – Where the mass flow of fluid passing through a flow meter (A) is equal to the fluid density (r) multiplied by the volume of the fluid (Q).

 

Different types of flow meter

There are a number of different types of flow meter available, each one suited to a different purpose, but always with the same goal of measuring the flow of a fluid or gas through a pipe.

  • Positive displacement flow meters: As the only meters to measure the actual volume, positive displacement meters work by repeatedly filling and discharging fluids from a chamber. Also known as volumetric flow meters, or rotary piston meters due to the way in which they operate.

    Rotary Piston flow meter with Hub connectors
    Rotary Piston Positive Displacement flow meter with Hub connectors
  • Inferential flow meters: These types of meters don’t measure volume, mass, or velocity. Instead they measure the flow of a fluid by inferring its value from other measured parameters such as differential pressure.
  • Velocity flow meters: The flow of fluid through the pipe is measured by the velocity of the flowing stream in order to determine the volume of the flow.
  • Mass flow meters: A mass flow meter, also known as an inertial flow meter, measures the flow rate of the mass of fluid as it travels past a fixed point during a specified unit of time.

 

What type of flow meter do I need?

There is no one-size-fits-all solution when it comes to flow meters. It largely depends on the industry you’re in, and what the flow meter will be used for. Here at Litre Meter we’re the flow meter experts, so we can help you to choose which type will work best for your needs, but here are a few questions to ask yourself before looking into purchasing a flow meter for your company:

  • What gas or liquid do I want to measure?
  • What level of accuracy do I require?
  • What is the temperature and viscosity of the fluid?
  • Does the fluid flow continuously or intermittently?
  • Will the meter be mounted in a safe or hazardous location?
  • What are the minimum and maximum flow rates?
  • What is the maximum pressure at the location?
  • What level of pressure drop is allowable?
  • Is the fluid compatible with the materials used in the flow meter?

Each type of flow meter has a different set of applications and constraints, so the best way to choose the right one is to use the application of the equipment, rather than the technology, to guide you in your choice. Once you know the answers to some or all of these questions speak to us and we can help you to determine which flow meter will best suit your needs.

The versatile VFF

Litre Meter was founded 40 years ago as a manufacturer of industrial flowmeters. Today, the company still manufactures flowmeters, but with a slight shift in focus – more than 80% of its products are designed specifically for the harsh conditions of the offshore oil and gas industry.


The shift towards offshore supplying happened largely due to Litre Meter’s ability to engineer new products, as many offshore oil and gas rigs require custom-built flow measurement solutions for chemical injection; however, the ability to engineer new products has sometimes been a setback for Litre Meter, as the majority of orders would often require custom engineering despite the company’s extensive catalogue of standard products.

Litre Meter defines its company by the strapline, ‘Specialist flow measurement engineering’, representing four of its unique and client-oriented company principles:

  • Specialist: Litre Meter is a specialist manufacturing company, focusing solely on products for measuring flow, rather than level or pressure.
  • Flow: its products drill down into the finer flow details, such as flow rate and flow total.
  • Measurement: its products measure flow accurately – they are not flow switches or flow indicators.
  • Engineering: although it offers a catalogue of standard products, Litre Meter can engineer bespoke solutions for unique challenges.

The VFF series

Litre Meter’s shift in focus began a little over 25 years ago, when it first adapted a standard industrial flowmeter for use on a North Sea oil rig. The popularity and success of this custom device led to the eventual production of their flagship range: the Viscous Fluids Flowmeter (VFF) series.

The VFF series is hugely popular and very adaptable, but its standard range has still been largely overshadowed by a flood of custom orders – until recently. One of the innovations for the 2015 range of VFFs included a new by-product: the FlowPod. The device itself is two-wire and fully HART compatible, with stainless steel housing. It opens up the popular VFF series to an even wider range of low-flow applications, and gives even the most obscure requirements near-instant access to Litre Meter’s innovative engineering without the need for custom designs.

Introducing the FlowPod

Flow Pod direct mount
The FlowPod mounts directly on the VFF flow meter.

Litre Meter decided quite early on that the FlowPod would be its only supporting instrument, and it has completely transformed the way the VFF range can be used.

Designed as Exi and Exd from the outset, the FlowPod was built in an enclosure small enough to be mounted directly onto the meter body, and gives Litre Meter an innovative method of incorporating extra functionality like reverse flow and redundancy measurement.
For Litre Meter, introducing the FlowPod to the VFF range was a great way to combine multiple design elements, gathered over 30 years of experience, to make an impressive and useful meter with a focus on utility plus weight and size reduction.
The 2015 VFF range includes more than 800 end-user drawings, representing more than 115,000 meter combinations and covering almost every conceivable possibility. While previously, around 80% of Litre Meter’s sales were for custom products, the introduction of the FlowPod means that only 5–10% of meters will now need any extra engineering at all. Most customers can simply access instant PDFs of general arrangement drawings, parts-list drawings and lifting diagrams, together with STEP files, as part of their Litre Meter quotation.
For Litre Meter, this means a faster sales cycle and more revenue; for the customer, it means much faster quotation, production and manufacturing times. 2015 has already been a big year for Litre Meter, and by raising its game and producing a range of meters without equals, it has truly cemented itself as a top-tier supplier of flowmeter technology to the chemical injection industry.

First published in Gas Technology Review www.gas-technology-review.com

 

New reed sensors now available

IMG_9574 sensor white bgWe have launched new sensor solutions to complement our revamped range of VFF flowmeters.

Our reed sensor package has been improved and now comes in a 316 stainless steel enclosure which is easy to install within the VFF range. The sensor comes complete with two reed switches that can be set for reverse flow detection or redundancy.

The sensor is tested to one billion pulses and environmentally tested in accordance with BS EN 13628-6: 2006. It is temperature rated to -20 to +80°C and it is available with the two or four wire Flowpod – the new explosion proof flow indication display unit for Litre Meter positive displacement flowmeters.

The non-wetted part has an M6 connector and the sensor is compact and designed for use at high pressures.

The new optional field sensor package comes in the same robust 316 stainless steel housing in order to make the sensors interchangeable with one another. The field sensor enables the output resolution of the VFF meter to be increased by a factor of twelve and it can still detect reverse flow.

Next Generation Flowmeters for Fluid Measurement and Control Solutions

Charles Wemyss, Litre Meter Limited

Types of Flowmeters fall into many categories. One could use the involvement of moving parts and electronics to define this. Mechanical meters, used and invented before domestic electricity was prevalent must be Old Generation. These would include what you and I have outside our houses for the measurement of domestic water. They would also include meters in our gas supply for the measurement of our consumption of gas. The very first turbine meters credited to Woltmann in 1790 were considered for calculating the loss of energy in open canals. It would be true to say that these were used for counting or totalising flow rather than providing an instantaneous rate display or output.

From the Old to the New

Those using electricity or electronics with a moving part like a rotor are also Old Generation as turbine meters have been around for several decades, for example. The first of these were axial turbine types developed, in essence from Woltmann, in the Second World War for accurately determining the fuel consumption of military aircraft and torpedoes. The pick-up or sensor with a magnet and rotating conductor enabled the number of rotations to be counted, totalised and used for rate display.
If we define Next Generation meters as having no moving parts so that the definition encompassed Thermal, Coriolis, Ultrasonic and Electromagnetic, then there would be a modern outlook. Apart from the fact that Faraday tried making an electromagnetic meter to measure the River Thames almost 200 years ago! He only failed because his instrumentation wasn’t sophisticated enough.
The obvious question to ask is: What is Next Generation, What is Current Generation and What is Old Generation? We can be certain that Old Generation does not mean unusable. We can also be certain that Old Generation in some people’s eyes is more than adequate for various tasks. This article explores the provenance of some flowmeter technologies, what might be round the corner and how to select the best meter for each project.

Some new and not-so-new flow measurement techniques:

New Technology

Coriolis, inertial force was first formulated by Gustave Coriolis in 1835 but MicroMotion didn’t release a commercial unit until 1977.

Electromagnetic, proven by Faraday but commercially produced from 1952. *Ultrasonic, from 1963.

Vortex, using the van Karmann effect of the generation of alternate vortices past a bluff body commercially from 1969, famously spotted by Leonardo da Vinci in 1504.

Thermal, hot wire anemometers were used from the early 1900s, commercially from the 70s.

Sonar, unconventional and measures turbulence since 2003.

Optical, measuring the speed and direction of individual particles using a laser beam, in research labs in the 70s and 80s but only commercially used in flare gases.

Traditional Technology

Differential Pressure like an orifice plate or Dall tube with a separate differential pressure transmitter. Also nozzles, pitots, Venturis and wedges. Still the most popular non-domestic meter type.

Positive Displacement, commercially pre 1830s for diaphragm gas meters with sheepskin diaphragms and sheet steel enclosures.

Turbine, first drawn up in 1790, commercially available post Second World War.

Variable Area, available for most of the 20th century.

Low Flow technology and the next ten years

There are various technologies that present themselves for low flow shown below. Many of the others mentioned elsewhere do not scale effectively.

Coriolis: Most manufacturers concentrate on ½” (15mm) and above. The issues of balance and producing thin wall tube to the required dimensional tolerances are hard to overcome. Smaller sizes exacerbate this.

Thermal: Microelectromechanical systems (MEMS), generally 0.01 mm to 0.1 mm in size, consist of a CMOS circuit on a thin silicon substrate. For lower flows these will replace a larger heated element and sensor. Liquids have a massively different thermal conductivity so the same device can measure at grams per hour rather than grams per minute.

Positive Displacement: Generally their purpose is to positively measure a trapped volume of fluid ? either gas or liquid. Gas versions tend to be for higher flows with the most popular one being used for domestic gas measurement. At lower flow the leakage between successive volumes is too large for effective measurement. For liquids where there is more viscosity the PD meters work well. Developments focus on some novel types and constant improvements to existing designs. There is a law of diminishing returns as the smaller the mechanical parts are, the harder they are to manufacture accurately. Also, leak paths are proportionally larger. One of the new types is the pendulum. This has one moving part with low mass and minimal friction loss, enabling it to respond to extremely low flow volume rates from 0.3 litres/hour. Unusually, this unit only works with viscosities up to 5 centiStokes. The rotary piston meter also has one moving part. In terms of flow rate, like most PDs, these prosper on viscosity. At 10 cSt a typical meter will start measuring at 0.08 l/h and when water is measured this increases to 0.4 l/hr.

In line ultrasonic: What happens when the pipes reduce in size and the type where a sensor is clamped on the outside of the pipe is no longer applicable? The sensors are mounted inside the pipe usually contrived in the shape of a U so that the ultrasound is passed between sensors at the base of the U. By knowing the diameter of the tube and the velocity between sensors, the volumetric flow can be calculated. Liquid flow rates down to 2 ml/min can be measured.

So if it’s not the methods of measurement we use that define Next Generation what is it? Perhaps: intelligence? The rise of smart meters i.e. those with digital communications and with the ability to self-verify are undoubtedly modern but were defined decades ago and have been in use for many years.

What’s Next?

Wireless communication is similarly up-to the- minute. HART digital communication has been around since the mid-1980s when it was developed by Rosemount Inc. for a range of measuring instruments, not just flowmeters. The HART foundation was formed in 1993 and the wireless version came along in 2007. So quite modern but Next?
So, is it the flowmeters that inhabit university laboratories and the R&D departments of flowmeter manufacturers that constitute Next Generation? Can we speculate what a cutting edge meter might look like in ten years’ time?

No Moving Parts

It would be fair to say that this Future meter would have no moving parts. This improves the chances of long term use as it would not suffer from mechanical degradation either planned or unplanned. It would ideally be non-invasive i.e. it would fit on the outside of a pipe and nothing would actually breakthrough the pipe wall. Currently, just ultrasonic meters match this criterion so let’s say that’s less than likely and the meter will therefore be non-intrusive. The sensor will break through the pipe wall but won’t impede the flow or perhaps just negligibly. What will the sensor measure, what techniques will it employ? That’s the $64,000 question. A single sensor is less likely as there will have to be a reference point for comparison.
Probably two sensors set apart, then, monitoring a property of the fluid. The clever part will be the intelligence of the signal processing; looking for perturbations in the signal amplitude and comparing it to the next sensor. Dumping thousands of comparisons for the sake of a few, locking onto patterns and pumping out high strength signals. In fact, the real hurdles will be firstly customer acceptance and secondly, electronic component obsolescence. Will the customer accept this meter and will it continue to find the small perturbations in property? Can he see it in action? Does he get a sense of goodness in the signal, in the rejection rate? What if the pipe vibrates, if the temperature ramps up, if the ‘property’ disappears? Then we find out that metering and measuring is about confidence, experience rather than Next Generation.

Bringing the Oil and Gas Industry Up-to-Date

The Oil & Gas industry is relatively conservative, relatively slow moving. The prevalence of HART and 4-20 mA signals decades after their introduction speaks volumes. Wireless, Bluetooth and fancy bus protocols are only just now making significant in-roads offshore. The creep of domestic innovation exemplified by the rise of the smart phone encourages instrument designers to bring their act up-to-date. Most instrumentation can only be compared with the most basic mobile phone. There is an inherent expectation that the modern user will have something easy-to-use, colourful and dangerously (?) customisable. The smartphone has many different uses of course beyond that of making calls. Arguably, it’s an instrument display in its own right. The logical conclusion is that the meter ‘display’ will be with the operator the whole time, in his/her hand. The obsolescence of components that bugs the subsea side of the industry is irrelevant in the actual instrument as this is replaced by the mobile phone and it’s ‘app’.
That still leaves the problem of the fast-moving world of miniature components for the clever parts – that will always be a thorn in the side of designers. Just as with most technologies, we’re not trying to design something to last for 30 years; the likelihood is that it will be overtaken by a new Next Generation device in ten years and then again in twenty years. All we can hope for is that the unit is still working in ten and twenty years and only needs replacing in thirty.
To select the best flowmeter for each application it is not just a question of looking up the first flowmeter you thought of on Google. Nor is it asking the engineer on the next desk or even consulting the internal specification guides issued by your employers. And it certainly shouldn’t be by selecting the cutting-edge meter of the day. It should be by consulting a flowmeter specialist – a specialist that has a wide range of solutions, not just one that is shoehorned into every application. Ideally, an independent specialist who can give unbiased advice and who will, if necessary, recommend an external solution.

Looking to the Future

In conclusion, the Next Generation of flowmeters is already operating, they’re already proven and they’re probably on the specification lists. Most applications can be met, more than adequately, by existing techniques. But the manufacturers aren’t standing still. They’re continually leveraging current technology with creeping demands. It’s more evolutionary than revolutionary but we’re all getting there – safely, economically and technically.

Chemical injection – from Africa to Arctic

Two articles in the current issue of Offshore magazine cover very different areas of the world ? West Africa and the Arctic.

They also cover very different scenarios. One is talking about ‘brownfield’ development – extending the life of existing fields and brining new reserves online through existing infrastructure. The other is focused on new technologies and challenges in safely exploiting hitherto unreachable reserves.

The common element is that both articles mention chemical injection as a key technology. This is, of course, an area in which Litre Meter has considerable experience.

Over the past year we have shipped a large number of meters to be used subsea, on a variety of chemicals, over a wide range of flows at high pressure and calibrated at specific viscosities. For example, Litre Meter rotary piston flow meters are part of systems used to control the amount of ‘antifreeze’ injected into pipelines at high pressure (430 bar) in subsea gas exploration on fields in the Caspian Sea and the North Sea.

‘Antifreeze’ fluids like methanol are used as thermodynamic inhibitors, which lower the freezing point of gas hydrate. They are injected into pipelines where there is a risk of hydrates (dew) forming then freezing at low temperature.

The antifreeze prevents gas hydrates solidifying as crystals and blocking pipelines – which can result in a costly shutdown and the risk of explosion or unintended release of hydrocarbons into the environment.

Litre Meter has also recently shipped flowmeters for use in chemical injection skids on a number of fields in the Gulf of Mexico and the Persian Gulf off Dubai. These meters are used in the flow measurement of wax dispersants and pour point depressants (PPD) to control their use to a very high tolerance.

Wax dispersants break apart and prevent the reformation of hydrocarbon sludge deposits and improve flow by reducing the viscosity of the fluid. PPDs are used to reduce the viscosity of oil and to maintain flow rate by preventing the build-up of wax crystals at low temperatures.

Sludge deposits are typically composed of varying concentrations of hydrocarbon, asphaltene, paraffin, water and inorganic materials. They are commonly found in storage tanks and vessels, production and transportation pipelines, process systems and hydrocarbon-producing formations where they have an adverse effect on the flow of crude oil from the well head.

Our expertise is nicely summarised in our new chemical injection brochure which highlights the enormous success of the VFF meter over the past few years in solving chemical injection measurement problems around the world.

With 3,000 VFFs in active use on chemical injection Litre Meter has demonstrated a depth of experience and knowledge that is unmatched in the low flow arena. The brochure provides further detail of the VFF range in one eight-page document.

Product labelling – QR codes, documentation access

We also unveiled a new electronic project documentation system. Details of each flowmeter supplied as part of a single project – for example, all the flow meters supplied for a particular chemical injection skid – will be held at a unique URL. The website will include items such as calibration certificates, PMI certificates and material certificates as well as specifications, manuals and instructions.

The address of the website will be printed on a chemical-resistant and wear-resistant label securely attached to each meter. The label will also carry a QR code linking to the website which will make it easy for service personnel on site to call up all the documentation on a smart phone by simply pointing it at the label. We believe most customers will note down the simple address and access it from a control room.

LM QR code
Litre Meter QR code allows remote access to documentation
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